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Structure of model peptides based on Nephila clavipes dragline silk spidroin (MaSp1) studied by 13C cross polarization/magic angle spinning NMR.

Yang M, Nakazawa Y, Yamauchi K, Knight D, Asakura T

Department of Biotechnology, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan.

To obtain detailed structural information for spider dragline spidroin (MaSp1), we prepared three versions of the consensus peptide GGLGGQGAGAAAAAAGGAGQGGYGGLGSQGAGR labeled with 13C at six different sites. The 13C CP/MAS NMR spectra were observed after treating the peptides with different reagents known to alter silk protein conformations. The conformation-dependent 13C NMR chemical shifts and peak deconvolution were used to determine the local structure and the fractional compositions of the conformations, respectively. After trifluoroacetic acid (solvent)/diethyl ether (coagulant) treatment, the N-terminal region of poly-Ala (PLA) sequence, Ala8 and Ala10, adopted predominantly the alpha-helix with a substantial amount of beta-sheet. The central region, Ala15, Ala18, and Leu26, and C-terminal region, Ala31, of the peptide were dominated by either 3(1)-helix or alpha-helix. There was no indication of beta-sheet, although peak broadening indicates that the torsion angle distribution is relatively large. After 9 M LiBr/dialysis treatment, three kinds of conformation, beta-sheet, random coil, and 3(1)-helix, appeared, in almost equal amounts of beta-sheet and random coil conformations for Ala8 and Ala10 residues and distorted 3(1)-helix at the central region of the peptide. In contrast, after formic acid/methanol and 8 M urea/acetonitrile treatments, all of the local structure tends to beta-sheet, although small amounts of random coil are also observed. The peak pattern of the Ala Cbeta carbon after 8 M urea/acetonitrile treatment is similar to the corresponding patterns of silk fiber from Bombyx mori and Samia cynthia ricini. We also synthesized a longer 13C-labeled peptide containing two PLA blocks and three Gly-rich blocks. After 8 M urea/acetonitrile treatment, the conformation pattern was closely similar to that of the shorter peptide.

Published 14 November 2005 in Biomacromolecules, 6(6): 3220-6.
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